From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 48C4E189905 for ; Sun, 15 Dec 2024 14:14:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734272095; cv=none; b=drZk7HeaMbJvc+2lZCN4MnTs0PKWU+80QRHCO48vtbtFUVLy57RFPzVfgjBAjd+JUwuBvoo+RoJHlMm36eL0oLELUF3gGBSR2l66ATbimlT14vvQX5n8Z3ssHwZXrRkB10/Y+2/Tg/A8lP4xlg9NgfrHrHebG4jBQ5iKJlBvo3c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734272095; c=relaxed/simple; bh=a53vNz4PUMmhwfydX5urPkZUSvWv4tcg1WmTFyd1Bk4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=K5tW2fuRJnaGUGljGubUqYtGyPvBMG8J85W12ROn5KQUNl0pYNz+X3ZT1S5/VwjjOfBmAHVlOm1S1R5DF/qEwvEsK/GWM3l464KePEix1m8NowVpIA4FFy1napKm2E2FavsAUhzpeP5m00UnLprCY2w8lQB9a9x0ww8D+3cBgi4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=ahDAvOwx; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ahDAvOwx" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1734272091; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=W3bWsES4HYFomsBdw8ix9WcXokymLmLN9+uEpumIVv4=; b=ahDAvOwxTWmBDOmDRYC/xsWFOjTRU5ng6ETmU4EVynvNfrRVyTHUnumU5HVq35F2unJkEW 9g+SfljyEOICaXR/IL/a59hSSvAH3NQRN5UKHMIj9Hsp/16uu9E5acEwzP+BS47PFZu+o3 v+4+83NuOVkOomktDDrme6BEV8GE5Ow= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-370-Ls14WX__PYqYc-D7LfhNYw-1; Sun, 15 Dec 2024 09:14:45 -0500 X-MC-Unique: Ls14WX__PYqYc-D7LfhNYw-1 X-Mimecast-MFC-AGG-ID: Ls14WX__PYqYc-D7LfhNYw Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 933201956089; Sun, 15 Dec 2024 14:14:42 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.41]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 295B630044C1; Sun, 15 Dec 2024 14:14:36 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 15 Dec 2024 15:14:19 +0100 (CET) Date: Sun, 15 Dec 2024 15:14:13 +0100 From: Oleg Nesterov To: David Laight Cc: 'Jiri Olsa' , Peter Zijlstra , Andrii Nakryiko , "bpf@vger.kernel.org" , Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire , "linux-kernel@vger.kernel.org" , "linux-trace-kernel@vger.kernel.org" Subject: Re: [PATCH bpf-next 08/13] uprobes/x86: Add support to optimize uprobes Message-ID: <20241215141412.GA13580@redhat.com> References: <20241211133403.208920-1-jolsa@kernel.org> <20241211133403.208920-9-jolsa@kernel.org> <1521ff93bc0649b0aade9cfc444929ca@AcuMS.aculab.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1521ff93bc0649b0aade9cfc444929ca@AcuMS.aculab.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 12/15, David Laight wrote: > > From: Jiri Olsa > > The optimized uprobe path > > > > - checks the original instruction is 5-byte nop (plus other checks) > > - adds (or uses existing) user space trampoline and overwrites original > > instruction (5-byte nop) with call to user space trampoline > > - the user space trampoline executes uprobe syscall that calls related uprobe > > consumers > > - trampoline returns back to next instruction > ... > > How on earth can you safely overwrite a randomly aligned 5 byte instruction > that might be being prefetched and executed by another thread of the > same process. uprobe_write_opcode() doesn't overwrite the instruction in place. It creates the new page with the same content, overwrites the probed insn in that page, then calls __replace_page(). Oleg.